Collisions of vehicles with obstacles have some conceivable patterns. It is conceivable that an obstacle after striking the front bumper of a vehicle again strikes another portion of the vehicle. The first collision of the obstacle with the front bumper is called a “primary collision,” and the next collision with another portion of the vehicle is called a “secondary collision.”
There is an airbag device with an airbag which is inflated with gas generated by an inflator immediately after a primary collision, covering a vehicle outside portion such as an A-pillar or a windshield, and mitigating an impact in a secondary collision of an obstacle with the vehicle outside portion.
When collided by an obstacle, an airbag having a high internal pressure for mitigating a secondary collision of the obstacle, however, can fail to sufficiently mitigate an impact on the obstacle. To solve the problem, a method of reducing an internal pressure by releasing gas within an airbag outside upon collision of an obstacle with the airbag seems possible.
To release gas within an airbag outside, it is required to provide a vent hole in the airbag to release gas by use of an internal pressure for inflating the airbag, for example.
A vehicle having a relatively long distance between the front bumper and the windshield, however, causes an obstacle to take a relatively long period of time between a primary collision with the front bumper and a secondary collision with the airbag. During that period, gas within the airbag is continuously discharged through the vent hole.
It is thus required to feed a large amount of gas into the airbag in view of a discharged amount of gas so as to keep the airbag in an inflated state. It is, however, required to increase the gas supply capacity of an inflator to feed a large amount of gas into the airbag, preventing reduction in size of the airbag device.
As a method for solving the problem, JP-A-11-334520 discloses an “Airbag Device,” for example.
This airbag device has a control valve switched between energization and de-energization for opening and closing a vent hole, an internal pressure sensor for detecting the internal pressure of an airbag to control the control valve, and a controller for controlling the control valve.
In the above device, when the airbag starts inflating, the vent hole is closed by the control valve. When an obstacle secondarily collides with the airbag after completion of inflation of the airbag, increasing the internal pressure thereof to a predetermined value, the sensor detects the internal pressure of the airbag and the control valve is actuated based on the detection signal, opening the vent hole. In this manner, it is possible not to discharge gas through the vent hole when the airbag starts inflating upon a collision of the vehicle with an obstacle, and to release gas outside through the vent hole when the obstacle is in a secondary collision with the airbag. The discharged amount of gas can thus be reduced to reduce the capacity of the inflator. In addition, the release of gas outside through the vent hole in the secondary collision of the obstacle with the airbag allows efficient mitigation of impact on the obstacle.
As stated above, the use of the airbag device in JP-A-11-334520 can provide sufficient effects in the reduction of capacity of the inflator and also the efficient absorption of impact on an obstacle.
This airbag device, however, needs to be provided with the internal pressure sensor, control valve and controller which are likely to relatively complicate the structure of the airbag device, preventing size reduction of the airbag device.
In this context, an airbag device being capable of efficiently mitigating an impact on an obstacle and having a simplified structure for size reduction is desired.